1. Field of the Invention
The present invention relates to optical fibers and, more particularly, to a method for forming optical fiber preforms and optical fibers therefrom.
2. Prior Art
Optical fibers typically include an optical energy transmitting core having a selected index of refraction surrounded by a cladding having an index of refraction lower than that of the core. When optical fibers are coupled to one another, they are ususally butt coupled or laterally coupled. With butt coupling, the ends of the fibers are usually cut transverse to the longitudinal axis of the fiber and joined in an end-to-end relationship. The alignment between the butt coupled fibers must be precisely controlled to produce the desired core-to-core registration. The alignment problem is particularly critical with single-mode fibers which can have core diamters of between 1 and 5 microns. As can be appreciated, a 1 or 2 micron lateral misalignment between butt coupled single-mode fibers can result in a substantial transimssion loss across the coupling. With lateral coupling, the fibers are placed in a side-to-side relationship with one another with energy transfer effected through evanescent field coupling between the laterally adjacent fibers. In general, the level of precision required for lateral coupling is less than that required for end-to-end butt coupling.
The techniques of lateral coupling have been greatly facilitated by the development of optical fibers, such as those disclosed in U.S. Pat. No. 4,315,666, that are rotationally non-symmetric along their length, for example, by placement of the core eccentrically in the fiber.